1. Field of the Invention
The present invention relates to an automatic balancing apparatus and a motor with a function to cancel rotational unbalances of a rotary body.
2. Description of Related Art
Automatic balancing apparatuses are often implemented in various rotary driving apparatuses that are used in industrial machines, home electric appliances, computers and the like. An automatic balancing apparatus is employed in a rotary body such as a rotary driving apparatus including a rotor shaft to cancel out rotational unbalances of the rotary body. Japanese laid-open patent applications HEI 10-257710 and HEI 11-178272 describe such automatic balancing apparatuses.
For example, Japanese laid-open patent application HEI 10-257710 describes a balancing member 3 provided about a rotor shaft of a motor 1, as shown in FIG. 12. The balancing member 3 is formed from a disc-like case body having an internal space provided therein. Plural ball members 4 are movably disposed within the space of the balancing member 3. When the rotational speed of the motor 1 exceeds its resonant rotational speed CR, the ball members 4 start moving in an opposite direction with respect to the position of center of gravity of a rotator body that includes the rotor shaft 2 and the balancing member 3, to thereby balance the rotator body. As a result, vibrations of the rotator body are reduced and the rotation thereof is stabilized.
However, in the automatic balancing apparatus described above, the plural ball members 4 tend to become unstable when the rotational speed of the motor 1 is below the resonant rotational speed CR, such that the ball members 4 collide against one another and make colliding noises and may be damaged. Moreover, the contact resistance among the ball members 4 becomes large at high-speed rotations when the viscosity of flowing air increases. As a result, the ball members 4 cannot be accurately disposed at appropriate balancing positions, and thus the rotary body cannot be sufficiently stabilized.
An automatic balancing apparatus described in Japanese laid-open patent application HEI 11-178272 has fan-shaped balancing members 5 rotatably disposed about a rotor shaft 6, as shown in FIG. 13. The automatic balancing apparatus described in Japanese laid-open patent application HEI 11-178272 generally solves the problems described above.
However, in the automatic balancing apparatus of the Japanese laid-open patent application HEI 11-178272, each of the balancing members 5 has a generally fan-like shape as viewed in plan, and therefore has to be made relatively large. This results in a problem in that the overall size of the automatic balancing apparatus becomes large.
It is an object of the present invention to provide an automatic balancing apparatus having a smaller and simplified structure that achieves an optimum balance correction action of balancing members.
It is another object of the present invention to provide an automatic balancing apparatus that has an improved rotational stability particularly at a low rotational speed range.
In accordance with one embodiment of the present invention, an automatic balancing apparatus may have a plurality of balancing members rotatable about the axis of rotation, each of the balancing members having a balance action section spaced a specified distance in a radial direction from the axis of rotation and a connection section that rotatably couples the balance action section to the axis of rotation. The balance action section has a mass that effects a balance correction action, and the connection section has a mass that substantially does not affect the balance correction action compared to the balance action section.
By the embodiment of the present invention having the structure described above, the center of gravity of each of the balancing members is shifted more outwardly from the rotor shaft in the radial direction compared to the conventional automatic balancing apparatus having fan-shaped balancing members, such as the one described in Japanese laid-open patent application HEI 11-178272. As a result, a smaller sized automatic balancing apparatus can achieve a better balance correction action.
In accordance with one embodiment of the present invention, the balance action section may have a balance storage section having an outer abutting surface and a balancing mass freely moveable in the balance storage section. The abutting surface may be in an arcuate form. The balancing mass is supported by the abutting surface when a rotator body on which the automatic balancing apparatus is mounted is operated at speeds that exceed a resonant rotational speed CR of the rotator body. As a result, the center of gravity of the balancing member is further shifted outwardly in the radial direction, and therefore a further miniaturization can be achieved.
The balancing mass may be formed from a globular body such as a ball that can readily move in response to a rotational unbalance. As a result, the sensitivity in the balance correction action can be increased. Also, each of the balancing members may be provided with a single globular body, such that the globular bodies are disposed isolated from one another. Accordingly, there is no collision between the globular bodies, and therefore generation of noises and damages to the globular bodies can be securely prevented.
In accordance with one embodiment of the present invention, the balance storage section has a retaining recessed section that retains the balancing mass in a region closer to the axis of rotation than the outer abutting surface in a low rotational speed range below the resonant rotational speed CR. The retaining recessed section may be provided with a step difference having a height in which the balancing mass can move out of the step difference of the retaining recessed section by a centrifugal force generated when the rotator body rotates at a speed exceeding the resonant rotational speed CR thereof. As a result, when the rotator body rotates in a low rotational speed range below the resonant rotational speed CR thereof, the balancing mass is retained in the retaining recessed section in a balanced state. As a result, when the rotator body starts its rotational operation again or in the low rotational speed range, the rotator body stably rotates in the balanced state.
In accordance with one embodiment of the present invention, the balancing mass may be formed from liquid that can freely change its configuration. As a result, the balance storage section can also be changed to any appropriate shape, which improves the degree of freedom in designs.
In accordance with one embodiment of the present invention, the balance action section may be formed from a solid metal weight that is attached to an outer end section of the connection section that extends in the radial direction. As a result, the center of gravity of the balancing member is further shifted outwardly in the radial direction by the metal weight, and therefore a further miniaturization can be achieved.
In accordance with one embodiment of the present invention, an automatic balancing apparatus may have a plurality of balancing members rotatable about the axis of rotation, each of the balancing members having a circular main body rotatable about the axis of rotation and an unbalance section that is formed by removing a portion of the circular main body.
As a result, a mass required for a balance correction action can be effectively secured along an entire peripheral region of the circular main body section. As a result, the automatic balancing apparatus of the present invention can be reduced in size and thickness for a given mass, compared to the conventional apparatus having fan-shaped balancing members having the same mass. Accordingly, the entire structure of the apparatus can be reduced in size and thickness.
By the use of the circular main body, an extreme cantilever structure of the conventional apparatus can be eliminated, and therefore highly stable rotational operations can be obtained from a low rotational speed state to a high rotational speed state. Accordingly, an excellent balance correction action of the balancing members can be achieved with a simplified and smaller structure, and also the rotation stability is improved.
In accordance with one embodiment of the present invention, the unbalance section is defined by a recessed section formed by removing a portion of the circular main body. The recessed section may be a through hole formed in the circular main body. As a result, even when the size of the unbalance section is changed, its center of gravity does not change, and therefore the mass of the balancing member is readily adjusted.
In accordance with one embodiment of the present invention, each of the balancing members may have a central circular section rotatable about the axis of rotation, an unbalance section spaced a distance from the axis of rotation and a connection section that connects the unbalance section to the central circular section. The unbalance section has a mass that effects the balance correction action, and the central circular section may have a mass greater than the mass of the unbalance section. As a result, an extreme cantilever structure of the conventional apparatus can be eliminated, and highly stable rotational operations can be obtained from a low rotational speed state to a high rotational speed state.
In accordance with one embodiment of the present invention, the automatic balancing apparatus may have a rotational retaining member that rotates the balancing members together with the rotary shaft in a low rotational speed region below the resonant rotational speed CR. In one embodiment, the rotational retaining member has a support section that is rotatable with the rotor shaft and a circular sliding-contact section provided on an outer periphery of the support section surrounding the entire periphery of the balancing members. The sliding-contact section may be in contact with the periphery of the balancing members. The sliding-contact section may be formed from a flexibly deformable material that is in contact with an outer periphery of each of the balancing members in the low rotational speed region and separated outwardly in the radial direction from the peripheral surface of each of the balancing members in a high rotational speed region exceeding the resonant rotational speed CR.
Since the rotational retaining member has the circular sliding-contact section that surrounds the entire periphery of the balancing members, the balancing members can be retained by the rotation retaining section no matter what angular positions the balancing members are located. Therefore, once the balancing members are placed in a balanced state, the sliding-contact section retains the balancing members in the balanced state even at a start of a next rotational operation of the rotator body. As a result, the rotation stability is improved particularly in the low rotation speed region, and the balancing members can move smoothly and quickly in a short time to appropriate locations for balancing actions in the high rotation speed region.
In accordance with one embodiment of the present invention, the plurality of balancing members may include a pair of balancing members provided in the axial direction and the rotational retaining member may include a pair of rotational retaining members provided opposing to each other in the axial direction for the pair of balancing members, respectively. Each of the circular sliding-contact sections of the rotational retaining members may include sliding-contact segments. The sliding-contact segments of one of the rotational retaining members and the sliding-contact segments of the other of the rotational retaining members may be alternately disposed in a peripheral direction in a non-contact manner. As a result, the pair of the rotational retaining members evenly exert the retaining actions on the pair of the corresponding balancing members, respectively, such that the balance correction action is more accurately achieved.
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention.